It is well established in current ophthalmic literature that extracapsular cataract surgery is the preferred method of cataract removal. A crude form of extracapsular surgery was performed in the nineteenth century but was abandoned in favor of intracapsular cataract surgery in the first half of the twentieth century. Two factors, however, led to the rebirth of the extracapsular technique for cataract removal in the early 1970's.
The first factor was the development of the operating microscope with coaxial illumination. The second factor was the development of machinery to provide simultaneous irrigation and aspiration for use in a closed-eye microsurgical system along with instrumentation adequate to perform this task. Such instrumentation is disclosed in U.S. Pat. Nos. 4,386,927 and 4,377,897 to Eichenbaum, and 4,369,785 to Rehkopf et al, the disclosure of which are incorporated herein by reference.
Vitreous surgery requires irrigation-aspiration equipment that includes some form of knife blade to cut the vitreous strands, all performed through a 3 mm incision in the pars plana. These cutting devices are also used for lens removal through the pars plana or limbus when necessary. It is, therefore, natural to search for a cataract removal technique that would allow routine cataract removal through an equally small incision. While cortical material can be easily aspirated, a means must be used to break up the harder lens nucleus.
One early device having such means was the phacoemulsification system which introduced an ultrasonically driven, vibrating needle as a means of breaking up the hard lens nucleus, allowing cataract removal through a 3 mm incision in the limbus. The phacoemulsifier along with the two above-mentioned factors spearheaded the move toward extracapsular surgery. After an initial growth in phacoemulsification, however, use of the technique leveled off and it is now used by a relatively small group of surgeons for several reasons.
First, the technique is difficult to perform, requiring a skill level greater than that achieved by the majority of surgeons. Second, currently available equipment can damage adjacent intraocular structures due to heat and vibration of the ultrasonic needle. Finally, the necessity of enlarging the incision to accommodate intraocular lens implants eliminates the advantage of a 3 mm incision.
Recognizing the advantages of extracapsular cataract surgery, therefore, the majority of ophthalmic surgeons began to perform extracapsular surgery by expressing the intact nucleus and using irrigation-aspiration equipment only to remove the cortex. Most surgeons do not feel comfortable trying to hold and control a bulky phacoemulsifier handpiece on the end of which sits an exposed needle vibrating in the confined space of the anterior chamber.
Recently, the use of lasers to perform eye surgery has also increased, as evidenced by the growing number of patents disclosing such use. Among these are U.S. Pat. Nos. 4,517,974 and 4,537,193 to Tanner; 4,564,011 to Goldman; 4,273,109 to Enderby; 4,122,853 to Smith; 3,982,541 to L'Esperance, Jr.; 3,865,113 to Sharon et al; 3,858,577 to Bass et al; 3,843,865 to Nath; 3,821,510 to Muncheryan; German Pat. No. 3,209,444 to Renz; and published European Patent Application No. 33,958 to Atsumi et al. Thus, it is logical to expect that the ultrasonic vibrating needle of the phacoemulsification system would give way to the current trend of using lasers. However, to date no acceptable laser surgical devices have been developed for use in extracapsular cataract surgery. The lack of such surgical devices reflects the difficult task of satisfying the required design parameters. Such parameters require an instrument to be: (1) capable of operating through a small incision; (2) able to direct the fragmenting energy directly and accurately to a very small area; (3) capable of preventing random laser or heat energy from damaging adjacent areas of the eye during an operation; and (4) configured to provide a sufficiently large opening to accommodate large, hard pieces of lens, while at the same time preventing unacceptably high levels of aspiration.
Additionally, due to the extremely high expense of such surgical equipment, it is greatly desirable to have a laser surgical system which can facilitate other types of laser surgery such as vitreous surgery. Thus, not only must the above parameters be satisfied, but the system must be designed to be as versatile as possible. This is especially true when different types of ocular surgery must be performed during a single operation. In such situations, the surgeon must be able to quickly and easily switch back and forth between different types of surgical instruments.